Currently, touch panels are well known input devices, which are widely arranged in liquid crystal displays or cathode ray tubes or other displays so that users can input signals by touching the screens of the displays. The touch panel generally has two conductive films which are separated with a gap. At least one conductive film is installed to a flexible transparent film and another conductive film is installed to a surface of a hard substrate. A plurality of plane adhesive strips are installed between the two conductive films. Adhesive areas are left for being coated with glue for combining the two conductive films.
The surface of the conductive film has a conductive layer deposited with conductive material, such as indium tin oxide (ITO) and the signals of the conductive film 1 are electrically connected to the silver-containing conductive electrode at the lateral sides of the conductive film. For example referring to FIG. 3, the conductive film T has a first portion P1. A signal is triggered from P1. The signal is transferred to the silver-containing conductive electrode R through a shortest first path D1 and then the signal is transferred to an M end of the silver-containing conductive electrode from the first signal input point K1 and then is transferred out. Similarly, the signal triggered from a second portion P2 of the conductive film 1 is transferred to the silver-containing conductive electrode from a shortest second path D2 and then is transferred to the M end of the silver-containing conductive electrode from the second signal input point K2 and then is transferred out. Thus from above description, it is known that the signals triggered on the conductive film are transferred to the succeeding signal processing circuit from different transfer paths. However since the general silver-containing conductive electrode is a long plane thin stripe which is arranged on a lateral edge of the conductive film and the silver-containing conductive electrode has a higher impedance. In the process of transferring the impedance signal, the signal will decay. Therefore, the signals will decay in transformation. When the signals transfer from points K1, K2 to M, the signals suffer from different impedances and then the decays of the signals are different. Especially, the impedances of signals are different from the farthest portion Kx to the point M and from the shortest portion Ky to the point M. This difference will affect the positioning on the touch panel and thus will affect the proceeding signal processing. Thus a compensation and calibration process is added so as to have signals matching the requirement.
In many prior art calibration methods, complicated conductive patterns are used to re-distribute the signals or a signal compensation circuit is further added to the silver-containing conductive electrode to control the re-distribute signals and thus to reduce non-uniform signal decays in the transformation of the signals. In U.S. Pat. Nos. 4,293,734, and 4,661,655, the compensation circuits are disclosed. As shown in FIGS. 4 and 5, complicated conductive pattern electrodes are installed at an edge of the conductive film T, which is specially designed. The electrodes have different shapes or lengths and a plurality of electrodes are installed near a middle section so as to reduce the decay in signal transformation and thus the voltage difference between two ends of the electrodes and the center portion thereof. However it is difficult to design the complicated pattern circuit and thus the calibration of the signal is not so precise. Moreover, errors are generated in the manufacturing process and thus imprecise signal calibration occurs. Furthermore, the pattern circuit causes that the area of the touch panel reduce. Besides, in other method of signal calibration, non-parallel curved lines are installed at edges of the conductive film T as a bus-bar R, such as those illustrated in FIG. 6. By this kind of bowed equipotential field bow bar, the signal is calibrated. This prior art is simple, but the bow bar will make the signal output end narrows and thus signal is greatly decayed. Furthermore, the curved edge of the bow bar will make the appearance of the touch panel unbeautiful and the working area of the touch panel is reduced.